This invention relates to the field of keyboard assemblies and keyboard switch mechanisms. More particularly, this invention relates to a new and improved keyboard assembly and keyboard switch mechanism in which the key switches are an array of flat topped protusions in an insulating sheet having contoured conductive patterns, the protrusions operating in a snap action manner to provide pronounced tactile feedback to the keyboard operator.
In the past several years there has been a considerable increase in the market for keyboard type devices. The hand-held calculator has probably been the largest selling product of this type, but there are many other product areas where the use of electrical keyboard devices is expanding, such as computer and data terminals, and telephones, to mention only a few. Particularly in the hand-held computer market, price competition has emphasized the need to reduce the cost of these devices while retaining performance characteristics and reliability. One of the most important performance and reliability characteristics of these devices is known as tactile feel or tactile feedback, i.e. the physical sensation fed back to the finger of the operator indicating that the electrical circuit has been successfully completed upon depression of the key switch.
There have been recent proposals to form keyboard switching arrays by forming domes in an insulating sheet having conductive paths formed thereon. Switching arrays of this type have the potential to be much more economical than individual keys typically used in keyboard devices. However, these domed arrays have heretofore had particularly acute problems in providing the desired snap action or tactile feedback. One particular keyboard switch assembly with dome shaped actuators is shown in U.S. Pat. No. 3,860,771. That patent shows a configuration in which the keyboard switches are domed elements; i.e., domed elements having a distinct convex curvature when viewed from the top side, i.e. the side on which actuating force is applied. The description in U.S. Pat. No. 3,860,771 purports to disclose structure which provides snap action and tactile feedback. However, attempts to make a device in accordance with the disclosure of U.S. Pat. No. 3,860,771 with the switch array secured between the individual switching elements and using a hinged keyboard have failed to produce a device with snap action and tactile feedback. The ability to use a hinged key configuration is very important, because a keyboard having hinged keys is very economical to produce since it can be formed in a single molding operation and requires no separate assembly of the keys. Thus, the inability of the structure of U.S. Pat. No. 3,860,771 to operate in a hinged key environment is an extremely serious shortcoming and deficiency.
There have been several other disclosures in the prior art of domed keyboards, all of these being for configurations having concave domes such as in U.S. Pat. No. 3,860,771. In this regard, reference is made to IBM Technical Disclosure Bulletin, Hayes and Knapp, "Snap-Action Membrane Switch Keyboard", Vol. 7, No. 12, p. 1168, May 1965 and U.S. Pat. Nos. 3,898,421; 3,643,041; 3,590,195 and 486,212. Attention is also directed to U.S. Pat. Nos. 3,780,237; 3,699,294; 3,383,487 and 2,138,549. Although the foregoing enumerated references are not intended to be a list of all of the prior art known to applicant, they represent the most pertinent prior art presently known to applicant.